1. Technical Field
The present invention relates to a motion sensing apparatus, and more particularly to a microwave based motion sensing apparatus wherein a single microwave sensor is employed for detecting multiple levels of motion.
2. Discussion
Motion sensors are presently employed in a wide variety of applications. Many of these motion sensors are based upon a microwave transceiver which emits and analyzes microwave signals in the 24 GHz range. An exemplary application is the use of a motion sensor for automatically opening a doorway as the motion of a pedestrian or vehicle approaching the doorway is detected. Once the pedestrian or vehicle is detected within the operating range of the motion sensor, the doorway is automatically opened and maintained in the open state for a predetermined amount of time, or until no more motion is detected.
The motion sensors known within the prior art generally work well for detecting the initial level of motion for triggering an event such as opening the doorway. Typically, these motion sensors operate at a single threshold level and are unable to adapt to different operating conditions, or switch between various operating modes for detecting multiple levels of motion. The current ANSI standard for detecting motion sets the minimum motion threshold at a rate of two inches of motion per second in a direction normal to the motion sensor. Motion detectors adopting this standard must be able to detect motion at this minimum level for triggering an event such as opening the door.
Additionally, various problems and challenges arise once the motion sensor has initially opened the doorway. For example, the doorway must be maintained in the open position until the pedestrian or vehicle passes completely through the doorway. A pedestrian will typically approach the doorway more slowly than a motorized vehicle. Additionally, the physical condition of the pedestrian may dictate the amount of time it takes to pass completely through the doorway. The motion sensor must also account for both large adults and small children moving at various speeds as they approach the doorway.
One method for detecting very small levels of motion is to provide a second separate sensing device for detecting whether the pedestrian or vehicle is present or moving within the doorway or range of the door. The second sensor operates at a more sensitive motion threshold. As such, the door can be maintained in the open state until the secondary sensor detects that the door threshold or doorway is clear. For example, a pressure sensitive walkway can be installed for operating in conjunction with the motion sensor so that the presence of a pedestrian would prevent the door from closing. Alternatively, an infrared beam of light can be transmitted across the doorway to a receiving sensor for detecting the presence of a person or vehicle within the doorway.
Another solution found within the prior art is the use of a second microwave or infrared based sensor for detecting presence or smaller levels of motion within the door threshold or the range of the door after the primary motion sensor has opened the door. However, the second sensor must operate so that motion of the closing door will not again trigger the reopening of the door. Several techniques have been developed for successfully implementing such a device. However, these techniques still require two individual sensors for detecting multiple levels of motion, or at least the combination of one microwave sensor and a secondary sensing device as discussed above. Additionally, the employment of two separate sensors for detecting multiple levels of motion increases the cost of providing automatic doors, increases the complexity of the overall system operation and maintenance, and requires more complex control algorithms for safely and efficiently operating the automated doorway.
Accordingly, it is desirable to provide a motion sensing system utilizing a single microwave based motion sensing unit which is capable of both detecting the initial motion of an approaching target, and continue monitoring for significantly smaller levels of motion as the target continues approaching the doorway. Such a device would provide a motion sensor which automatically changes between multiple operating modes. It is further desirable to provide a system having a single motion sensor which can adaptively adjust the level or threshold of motion detected for sensing varying levels of motion of a pedestrian approaching the doorway. Finally, it is desirable to provide a motion sensing apparatus which is unaffected by the false motion of a closing door inadvertently triggering the reopening of the doorway.